To date capillary electrophoresis and microchannel chip electrophoresis have been widely researched since they are exceptionally good methods when separating and analyzing trace amounts of a biomolecule, and allow automatization and speed-up of analyses (Non-patent Document 1).
Materials generally used for capillary electrophoresis or microchannel chip electrophoresis include glass, but glass has many problems to be solved when separating proteins.
For example, capillary electrophoresis or microchannel chip electrophoresis apparatus made of glass is influenced by electroosmotic flow.
Thus, for example, to prevent the generation of electroosmotic flow inside capillaries, the inner walls of the capillaries have been coated with polymers (Patent Documents 1, 2, and 3). Coating methods including chemical immobilization of compounds onto surfaces and physical absorption have been attempted.
Coating with silane-coupling agents are known chemical coating methods when using glass capillaries or microchannel chips. These methods can very strongly coat the inside of microchannels since the silane-coupling agents bind covalently. However, homogenous coating is difficult, and capillaries or microchannel chips with high reproducibility cannot be produced. Further, the coating method uses chemical reactions and is thus difficult, making manufacturing processes ineffective.
Another known coating method is a physical coating method where the coating agent flows through the channels. For example, there are methods in which an electrophoresis buffer mixed with a coating agent flows through to coat the channels. These methods are very convenient, but since adsorption is based on electrostatic or hydrophobic interactions, the absorptive conditions are very weak and coatings can be easily detached, which is problematic. Further, since electrostatic interactions are easily influenced by pH, they have limited application.
Thus, methods for applying homogenous and stable coating on substrate surfaces are required. For example, the entire substrate surface of a chip with microchannels on the surface of a glass substrate has been coated with a plasma-polymerized membrane (Non-patent Document 2).
However, extremely high temperatures (e.g. 500° C. to 600° C.) are required when coating a glass substrate and a cover with a plasma-polymerized membrane, and there are cases where the plasma-polymerized membrane deteriorates upon attempting to laminate the substrate and cover using thermocompression bonding. Methods for using adhesives to bind substrates and cover materials have thus been adopted (Non-patent Document 2); however, use of adhesives can result in extrusion of the adhesive into microchannels, depending on the amount used or the site of application, and thus production processes controlling the amount of adhesive used, the sites of application, and the like can become complicated.
[Non-patent Document 1] Journal of Chromatography (F. E. P. Mikkers, F. M. Everaerts, Th. P. E. M. Veerheggen, J. Chromatogr.). 169, 11, 1979
[Non-patent Document 2] Analyst, 2003, 128, 237-244
[Patent Document 1] Japanese Patent Kohyo Publication No. (JP-A) H/S5-503989
[Patent Document 2] Japanese Patent Kohyo Publication No. (JP-A) H/S 7-506432
[Patent Document 3] Japanese Patent Kohyo Publication No. (JP-A) H/S 9-504375